Apparatus for continuous heat treatment of sheet or strip material



5 Sheets-Shet 1 .P'. AYERS 'SHEET OR STRIP MATERIAL Nov. 28, 1967APPARATUS FOR CONTINUOUS HEAT TREATMENT OF Filed May 22, 1963 APPARATUSFOR CONTINUOUS HEAT TREATMENT OF Filed May 22, 1963 SHEET OR ,STRIPMATERIAL 5 Sheets-Sheet 2 FIG-.4.

6 14a if 5 t mi FIGS.

6 Lam "Push IRAQ Nov. 28, 1967 APPARATUS FOR CONTINUOUS HEAT TREATMENTOF SHEET OR STRIP MATERIAL Filed May 22, 1963 P. AYERS 5 Sheets-Shed 5United States Patent 3,355,159 APPARATUS FOR CONTINUOUS HEAT TREAT- MENT0F SHEET OR STRIP MATERIAL Peter Ayers, High Wycombe, England, assignorto The British Aluminium Company Limited, London, England, a company ofGreat Britain Filed May 22, 1963, Ser. No. 282,378 Claims priority,application Great Britain, May 23, 1962, 19,867/ 62 Claims. (Cl. 266-3)This invention relates to improvements in the continuous heat treatmentof sheet or strip material (hereinafter referred to as strip material).

It is often desirable to heat strip material to some elevatedtemperature as rapidly as possible and immediately to cool it again. Inthe case of annealing of aluminium and aluminium alloy sheet, forexample, rapid heating of the metal to a suitable temperature, followedby a short holding time at that temperature, could lead to a fine grainsize, could minimise high temperature oxidation staining in these alloysprone to show this defect, and where ventilation is adequate couldeliminate oil staining. Rapid cooling of the metal immediately afterheat treatment would facilitate handling and would reduce thepossibility of mechanical damage during handling. The chief problemassociated with carrying out these operations continuously on stripmaterial, in many cases, lies in the transference of heat withsufficient speed, both to and from the strip, without at the same timecausing it mechanical damage.

Known methods for continuously heat treating strip material generallycomprised heating it by forced convection using air at a temperaturehigher than that to which it is desired to heat the strip; heating byradiant or by induction heating; or by a combination of these methods.Cooling is usually done by forced convection. However,

these methods suffer from certain disadvantages. If the strip stops forany reason, or if it changes speed, then overheating and damage to thestrip may result. Further, accurate control of the temperature of thestrip is difiicult to attain. Another known method for continuously heattreating strip material involves passing an electric currenttransversely through strip and making use of the resistance heating.This technique can only be successful if the material to be treatedpossesses a suitable electrical resistance, and it is very diflicult toarrange suitable electrical contacts at the edges of the strip.

It is an object of the present invention to provide an improved methodof and apparatus for continuously heat treating strip material wherebythe disadvantages referred to above shall be materially reduced orentirely obviated and whereby heat may be rapidly transferred to andfrom the strip material without mechanical damage to the latter.

According to one aspect of the present invention, a method ofcontinuously heat treating strip material comprises passing the strip insuccession through two fluidised beds, the first of which is at atemperature greater than the second, and maintaining the strip with itswider faces in substantially vertical planes during its passage throughthe beds.

Preferably, the strip is passed directly from the second bed into achamber supplied with gas under pressure to reduce any tendency of thesecond bed material to escape.

According to another aspect of the present invention, apparatus for heattreating strip material comprises two chambers for fluidisable material,an outlet slot from one chamber and an inlet slot to the other chamber,both slots being dimensioned and arranged to permit the passagetherethrough of the strip material with its wider faces contained insubstantially vertical planes, means for 3,355,159 Patented Nov. 28,1967 heating, and fluidising the fluidisable material in the one chamberand means for fluidising and cooling the fluidisable material in theother chamber According to one feature of this other aspect of thepresent invention, apparatus for heat treating strip material comprisesa container for fluidisable material having a partition defining twochambers and having a slot for the passage therethrough of the strip, aninlet slot to the first chamber to admit the strip thereto, an outletslot from the second chamber for the passage therethrough of the strip,means for heating and fluidising the fluidisable material in the firstchamber and means for fluidising and cooling the fluidisable material inthe second chamber, the inlet, outlet and partition slots being arrangedand dimensioned to permit the passage of the strip ma terialtherethrough with its wider faces contained in substantially verticalplanes.

Preferably, the outlet slot communicates directly with a gas chamberintended to be supplied with gas under pressure to reduce the tendencyof the fluidisable material in the second chamber to escape through theoutlet slot, the gas chamber having a further outlet slot for thepassage of the strip therethrough.

Advantageously, the outlet slot of the second chamber has a dimensionnormal to the wider faces of the strip which is substantially equal tothe thickness of strip plus twice the diameter or major dimension of thelargest particle of fluidisable material.

Desirably, the longitudinal edges of the inlet slot and the furtheroutlet slot are defined by a resilient material, e.g.polytetrafiuorethylene, which resilient material is arranged to bear onthe strip in its passage through the slot defined thereby.

Conveniently, the longitudinal edges of the outlet slot from the secondchamber are defined by a resilient material, e.g. rubber.

It is preferred to provide means for recycling to the second chamber anyfluidisable material escaping through the outlet slot to the gaschamber.

According to another feature of the second aspect of the invention,apparatus for heat treating strip material comprises two chambers forfluidisable material, an outlet slot in the floor of one chamber, aninlet slot in the floor of the other chamber, both slots beingdimensioned and arranged to :permit the passage therethrough of thestrip material with its wider faces contained in substantially verticalplanes, an intermediate chamber connecting the outlet and inlet slotsand defined by two spaced curvilinear walls, means for supplying fluidunder pressure to the intermediate chamber to cushion the stripmaterial, means for heating and fiuidising the fluidisable material inthe one chamber and means for fluidising and cooling the fluidisablematerial in the other chamber.

Some embodiments of the invention will now be described by way ofexample, reference being made to the accompanying drawings in which:

FIG. 1 is a somewhat diagrammaticlongitudinal sectional view of anapparatus according to the invention,

FIG. 2 is a transverse section taken on the line 11-41 of FIG. 1,

FIG. 3 is a fragmentary section taken on the line III-III of FIG. 1,

FIG. 4 is a fragmentary section taken on the line IV-IV of FIG. 1,

FIG. 5 is a fragmentary section taken on the line VV of FIG. 1,

FIG. 6 is a diagrammatic longitudinal section through an alternativeform of apparatus, and

FIG. 7 is a fragmentary section taken on the line VII-VII of FIG. 6.

The apparatus of this example comprises a container 1 divided into twochambers 2 and 3 by a partition 4 of heat insulating material, e.g.Sindanyo sheet, having a slot 5 therein for the free passagetherethrough of the strip 25 being treated. The chambers 2 and 3 contain0.5 mm. diameter glass ballotini (not shown) up to a level above theslot 5 and the container 1 has a false bottom provided by wire cloth 6to provide at the bottom of the container plenum chambers 7 and 8intended separately to be supplied with air under pressure from pipes 9'and 10 respectively in order to fluidise the glass ballotini in thechambers 2 and 3. The chamber 2 is provided with heaters 11 supported bypillars 11a and disposed on either side of the path of travel of thestrip through the chamber 2 (see FIG. 2') and inclined to the verticalso as to direct the fluidised medium towards the strip 25 passingthrough the chamber. The chamber 3 is provided with bafiies 12 supportedon pillars 12a and similarly arranged and also has a cooling pipe 13immersed in' the glass ballotini through which a cooling medium such aswater is intended to flow to extract heat from the fluidised bed.

The chamber 2 has an inlet slot 14 the vertical longitudinal edges ofwhich are defined by strips of resilient material 15- which, in thisexample, are strips of polytetrafluoroethylene. The strips 15 are springloaded by means of coil springs 16 and strip steel springs 17 so as tobear continuously on the sheet 25 as it enters the chamber 2 through theslot 14.

The chamber 3 has an outlet slot 18 the vertical longitudinal edges ofwhich are defined by a resilient material 19 such as rubber, the slothaving a dimension transverse to the wider face of the sheet or strip 25which is just suflicient to allow the passage of the strip through theslot 18 plus two of the largest particles of the glass ballotini placedside by side, i.e. this dimension is approximately 1 mm. plus thethickness of the sheet. The outlet slot 18 opens directly into a gaschamber .20 intended to be supplied with air under pressure along thepipe 21 so that there is an air flow from the chamber 20 through theslot 18 to the chamber 3 whereby the tendency of the glass ballotini toescape through the slot 18 is reduced. The lower end of the gas chamber20 is of inverted conical shape and communicates by way of a pipe 21with a cyclone separator 22, air being injected into the pipe 21 by wayof a further pipe 23 such that any of the glass ballotini which escapesinto the chamber 20 is returned to the chamber 3 along the pipe 21through the cyclone separator 22. An outlet slot 14a is provided to thechamber 20 and is similar in most respects to the inlet slot 14, likereference numerals followed by the suffix a being used to indicate likeparts. Adjacent the outlet slot 14a there is provided a pair of rubbercovered rollers 24 between the bite of which the strip 25 is passed to awinding coil.

As can be seen in FIGS. 1 and 2, the container 1 has a width normal thedirection of travel of the strip 25 which is small in relation to itsheight and its dimension parallel to the direction of travel of thestrip 25. This width is increased towards the open top of the containerto reduce the velocity of the air escaping therefrom.

In the operation of the apparatus described the glass ballotini in thechamber 2 is heated by the heating means 11 and fluidised by hot airsupplied from the pipe 9 to provide a fluidised bed which is maintainedat a selected temperature. The glass ballotini in the chamber 3 isfluidised by air at ambient temperature supplied by way of the pipe 10and heat is extracted from this fluidised bed both by the cold air flowand by the cold water flow along the pipe 13. The strip 25 to be heattreated is fed from a coil' (not shown) at a selected rate with itswider faces in substantially vertical planes through the inlet slot 14,through the chamber 2, through the slot 5 in the partition 4, throughthe chamber 3, through the outlet slot 18, through the chamber 20;through the further outlet slot 14a and between the rollers 16 to aconventional winding coil 16b. During the passage of the strip 25through the chamber 2 a rapid transfer of heat takes place to the stripand an equally rapid transfer of heat from the strip takes place in thechamber 3. The rate of travel of the strip is selected in accordancewith the nature of the heat treatment required.

Although any number of pulverulent materials may be suitable for use inthefluidised beds, the glass ballotini described has been found to bevery suitable as it does not adhere to the strip and there is little orno dust from the top of the. bed. The term ballotini is. a standard andrecognized term to define the pulverulent material which consists ofsmall spherical glass particles which are commonly known as ballotini.The term ballotini is Italian for small balls. Smaller particles can beemployed and this would reduce the quantity of air required forfluidisation. However, smaller particle sizes may increase thedifliculty of sealing at the inlet and outlet slots and of avoidingdamage to the sheet. Larger particles would require larger quantities ofair and would give poorer quality fluidisation.

Three examples of aluminium strip treated by the above process andapparatuswill now be described.

Example 1 A length of half hard temper NSS aluminium alloy strip 6 ins.wide and 0.01 in. thick was annealed in the apparatus described. This.alloy is one containing- 3.5% by weight of Magnesium and 0.4% by weightof manganese as alloying constituents. Each bed was 12 ins. long, 3 ins.Wide and 8 ins. deep, and the fluidised bed in the chamber 2 wasmaintained at a temperature of 370 C. The strip was fed: at a rate of 2ft. per minute and the properties of the annealed material were. asfollows: 0.1% proof stress 6.8-5 tons/sq. in.

U.T.S 14.4 tons/sq. in.

Elongation 18.0%.

Grains/mm. 2000.

Surface condition Free from mechanical damage.

Free fromoili staining. Free from: high temperature. oxidationdiscolouration.

Example 2 A length of hard temper 99.0% aluminium strip having the samedimensions as that described in Example 1. was fed at the same ratethrough. the same apparatus. but, in this case, the temperature of thefluidised bed in. the chamber 2 was maintained at 400 C. The propertiesof the annealed material were as follows:

0.1% proof stress 2.33 tons/sq. in.

U.T.S. 5.0 tons/sq. in.

Elongation 20%.

Grains/mm. 2000.

Surface condition Free from mechanical: damage;

U.T.S. 6.84tons/sq. in.

Elongation 28.5%.

Grains/mm. 2000.

Surface condition Free from mechanical damage.

Free from oil staining. Free from high temperature oxidationdiscolouration.

The alternative apparatus illustrated in FIGS. 6 and 7 comprises twoopen-topped spaced chambers 26 and 27 for fluidisable material eachhaving a false bottom 28 and 29 of Wire cloth or similar air-permeablematerial to provide plenum chambers 30 and 31 respectively at the bottomof each chamber. The floor of the chamber 26 is form-ed with ahorizontally extending slot 32, the direction of length of which isnormal to the direction in which the chambers 26 and 27 are spaced. Aninlet slot 33 is formed in the floor of the chamber 27 and extendsparallel to .the slot 32. An intermediate chamber. 34 connects the slots32 and 33 and is defined by two spaced Walls 35 and 36 which arecurvilinear about an axis substantially parallel to the direction oflength of the slots 32 and 33. The inner wall 35 is perforated anddefines a semi-cylindrical plenum chamber 37 closed by end plates 33(FIG. 7) which also close the intermediate chamber 34. Air inlet pipes39, 40, and 41 are respectively provided to the plenum chambers 30, 31,and 37. Heating means 42 similar to the heaters 11 of the previousexample, is provided in the chamber 26 on either side of the path oftravel of the metal strip indicated at 43 and cooling means (not shown)similar to the pipe 13 of the previous example, is disposed in thechamber 27.

In the operation of the apparatus described, the chambers 26 and 27 arepartly filled with glass ballotini which is fluidised by the airsupplied from the plenum chambers 30 and 31. The strip 43 is passedunder tension vertically downwards through the open-top of the chamber26 and out through the slot 32 in the floor thereof, through theintermediate chamber 34, up through the inlet slot 33 to the chamber 27and out through the open top of the latter. The air supplied to theplenum chamber 37 passes through the perforations in the inner wall 35of the intermediate chamber 34 to form a cushion of air which supportsthe metal strip during its passage through the intermediate chamber 34and prevents it touching the sides of the slots 32 and 33 or the wall 35and hence prevents mechanical damage to the strip 43. As the strip 43 isunder tension, any tendency to the formation of a double curvature ismaterially reduced so that the width of the slots 32 and 33 can be aminimum, e.g. equivalent to the thickness of the strip plus twice theaverage dimension of the glass ballotini. Air supplied to theintermediate chamber 34 escapes through the slots 32 and 33 andmaterially reduces any tendency of the fluidised beds in the chambers 26and 27 to escape through the respective slots. The strip, during itspassage through the fluidised beds in the chambers 26 and 27, has itswider faces disposed in substantially vertical planes and, during itspassage through the intermediate chamber 34 undergoes a 180 change inits direction of advance.

It is preferred to provide means for recycling any fluidised bedmaterial which escapes to the intermediate chamber 34, this being in theform of a pipe 44 extending from the chamber 34 to a cyclone separator(not shown) and means for returning the material from the separator toone or other or both of the beds.

What I claim is:

1. Apparatus for heat treating strip material comprising two chambersfor fluidisable material, an outlet slot from one chamber and an inletslot to the other chamber, both slots being dimensioned and arranged topermit the passage therethrough of the strip material with its widerfaces contained in substantially vertical planes, means for heating andfiuidising the fluidisable material in the one chamber and means forfluidising and cooling the fluidisable material in the other chamber.

2. Apparatus for heat treating strip material comprising two chambersfor fluidisable material, a first gas pervious fluidisable materialsupporting surface in one of said chambers defining a first plenumchamber, a second gas pervious fluidisable material supporting surfacein the other of said chambers defining a second plenum chamber, meansfor supplying gas under pressure 6 to said first plenum chamber tofluidise the fluidisable material in said one of said chambers, heatingmeans disposed in said one of said chambers, means for supplying gasunder pressure to said second plenum chamber to fluidise the fluidisablematerial in said other chamber,

heat extracting means disposed in said other chamber and means foradvancing the strip successively through both chambers with the widerfaces of the strip in substantially vertical planes.

3. Apparatus for heat treating strip material comprising first andsecond chambers for fluidisable material, a third chamber, a partitionwall between said second and third chambers, a vertically extending slotin said partition wall dimensioned to permit the passage of the striptherethrough with the wider faces thereof in substantially verticalplanes, a first gas pervious support in said first chamber defining afirst plenum chamber, a second gas pervious support in said secondchamber defining a second plenum chamber, heating means in said firstchamber, heat extracting means in said second chamber, means forsupplying gas under pressure to said first plenum chamber, means forsupplying gas under pressure to said second plenum chamber, means forsupplying gas under pressure to said third chamber to maintain thepressure in said third chamber at a level greater than that prevailingin said second chamber and means for advancing the strip through saidfirst, second and third chambers with the wider faces thereof insubstantially vertical planes.

4. Apparatus for heat treating strip material comprising a container, apartition wall of heat insulating material dividing said container intofirst and second chambers, a vertically extending slot in said partitionwall dimensioned to permit the passage therethrough of the strip withthe wider faces thereof in substantially vertical planes, a first gaspervious support in said first chamber defining a first plenum chamber,a first bed of fluidisable material in said first chamber supported onsaid first support and of a depth so as to extend to a level above saidpartition slot, means for supplying gas under pressure to said firstplenum chamber to fluidise said first bed, a vertically extending inletslot to said first chamber dimensioned to permit the passage of thestrip therethrough with the wider faces thereof in substantiallyvertical planes, strips of resilient material defining the verticaledges of said inlet slot and arranged to bear against the strip enteringsaid first chamber, heating means disposed in said first bed on eitherside of the path of travel of the strip between said inlet slot and saidpartition wall slot and arranged to direct the material of said firstfluidised bed towards said path of travel, a second gas-pervious supportin said second chamber defining a second plenum chamber, a second bed offluidisable material in said second chamber supported on said secondsupport and extending above the level of said partition slot, means forsupplying gas under pressure to said second plenum chamber to fluidisesaid second bed, a vertically extending outlet slot from said secondchamber dimensioned to permit the passage therethrough of said stripwith the wider faces thereof in substantially vertical planes, strips ofresilient material defining the longitudinal vertical edges of saidoutlet slot providing a horizontal dimension to said slot substantiallyequal to the thickness of said strip plus twice the major dimension ofthe largest particles of said second bed and heat extracting means insaid second bed.

5. Apparatus according to claim 4 including a third chamber into whichsaid outlet slot opens and means for maintaining the gas pressure insaid third chamber at a level greater than that prevailing in saidsecond chamber.

6. Apparatus according to claim 5 including means for returning fromsaid third chamber to said second chamber any of the fluidisablematerial escaping through said outlet slot.

7. Apparatus according to claim 4 including baffies disposedinsaidsecondv chamber on both. sides of. the path of travel of the. stripfrom the partition slot to the outlet. slot and arranged to direct thematerial of said secondbed towards said path. of. travel of the stripthrough said. second. chamber.

8. Apparatus for heat treating strip material comprising two chambersfor fluidisable material, an out-let slot in the floor of one. of saidchambers, an inlet slot in, the floor of the other of said chambers,both said slots being dimensioned and. arranged. to. permit the passagetherethroughof the. strip. with its. wider faces contained insubstantially vertical planes, an intermediate chamber connecting saidoutlet and. inlet. slots. and defined by two.

spaced curvilinear walls, means for supplying; fluid under pressure tosaid intermediate. chamber to cushion the strip material, means forheating and fiuidising the fluidisable material in said one chamber andmeans: for fiuidi'sing and cooling the fluidisable material in. saidother chamber.

9. Apparatus for heat treating; strip material comprising first andsecond chambers, a first gas permeable support in said first chamberdefining a first plenum chamber in the. lower part of said firstchamber, a first bed of. fluidisable. material in. said first chamber,means for supplying gasunder pressure to said first plenum chamber to'fluidise said. first bed, heating. means disposed in said first chamber,an outlet slot in the. floor of said first chamber to permit the passagetherethrough of the strip, a second gas permeable support in saidsecond'chamber defining a second plenum chamber in the lower part ofsaid. second chamber, a second bed of fluidisable material in said.second chamber, means for supplying gas under pressure tosaid second.plenum chamber tofiuidise said second bed, heat extracting, meansdisposed in said second bed, an inlet slot in: the floor of said second.chamber,. an intermediate chamber connecting said inlet and outlet slotsand defined by an inner perforatedcurvilinear wall. and an outercurvilinear wall, means for advancing the strip in. successionvertically downwards through said first chamber, through said outletslot, said intermediate chamber, said inlet slot and vertically upwardsthrough said second chamber and means for supplying through saidperforated inner wall to. said intermediate chamber a gas under apressure sufficient to maintain the strip out ofcontact with said innerWall.

10. Apparatus according to claim 9 including means for. recycling fromsaid intermediate chamber to at least one of said first and secondchambers any fluidisable material escaping to said intermediate chamber.

References Cited UNITED STATES PATENTS 1,646,498 10/1927' Seede 2663'1,671,810 5/1928 Caughey 2663 X 2,192,303 3/1940 Perm 266-3 2,957,68810/ 1960 Luecke 2663 3,053,704 9/ 1962 Munday 148-1 31 X 3,074,8281/1'963 Grifiin 14813.1 3,096,221 7/ 1963 Tanaka 148203 3,109,044 10/1963 Flowers 2663 FOREIGN PATENTS 144,447 12/ 1951 Australia. 906,349 9/1962 Great Britain. a

J. SPENCER OVERHOLSER, Primary Examiner.

D. L. RECK, Examiner. R. S. ANNEAR, D. L. REISDOREAssistant Examiners.

1. APPARATUS FOR HEAT TREATING STRIP MATERIAL COMPRISING TWO CHAMBERSFOR FLUIDISABLE MATERIAL, AN OUTLET SLOT FROM ONE CHAMBER AND AN INLETSLOT TO THE OTHER CHAMBER, BOTH SLOTS BEING DIMENSIONED AND ARRANGED TOPERMIT THE PASSAGE THERETHROUGH OF THE STRIP MATERIAL WITH ITS WIDERFACES CONTAINED IN SUBSTANTIALLY VERTICAL PLANES, MEANS FOR HEATING ANDFLUIDISING THE FLUIDISABLE MATERIAL IN THE ONE CHAMBER AND MEANS FORFLUIDISING AND COOLING THE FLUIDISABLE MATERIAL IN THE OTHER CHAMBER.